Heat exchanger



United States Patent 3,498,370 HEAT EXCHANGER Joseph E. Baggs, 5331 Harvard Ave., Westminster, Calif. 92683 Filed May 6, 1968, Ser. No. 749,893 Int. Cl. F28d 7/12 US. Cl. 165-156 6 Claims ABSTRACT OF THE DISCLOSURE Heat exchanger comprising an outer casing, a core member disposed axially within the casing, a spiral sheet positioned within the casing in the annular space between the inner wall of the casing and the core member, such spiral sheet extending axially of the casing, and a plurality of tubes positioned through the spiral sheet and disposed in an axial direction in said annular space in the casing. A fluid inlet is provided to the tubes which define a first fluid path, and a fluid outlet is provided at the opposite ends of the tubes, and a fluid inlet is also provided to the annular space between adjacent spirals of the spiral sheet which defines a second fluid path, and a fluid outlet is provided therefrom. The resulting heat exchanger has improved effectiveness and efiiciency, and is of relatively low cost and provides high reliability.

This invention relates to heat exchangers or heat transfer devices and is particularly concerned with counter-flow heat exchangers for applications in which optimum size,

effectiveness and high efiiciency are important, as for example, in refrigeration systems designed to produce very low temperatures, e.g. approaching absolute zero.

There are many systems and processes utilizing various types of heat-exchangers and counter-flow operation. The effectiveness, cost and size of such systems generally have been limited to the effectiveness, cost and size of the heat exchanger employed in the system.

When employed for example in refrigeration or cryogenic systems, a counter-flow heat exchanger is a device which employs the recirculation of a low temperature fluid to pre-cool incoming fluid of a higher temperature, or vice versa. For example, low temperature, and also low pressure fluid, having first served its primary refrigeration function in the system, is directed to the heat exchanger for utilization of any residual cooling capacity therein by heat transfer to a fluid of a higher temperature, and also, for example, having a higher pressure, to affect efiicient and economical cooling of the latter fluid.

Prior art heat exchangers often are limited in the amount of heat exchange surfaces associated with one or the other of the two fluid flow paths, the length over height ratio of the heat exchanger and/ or unit cost. A need accordingly exists for a heat exchanger with superior overall efficiency and effectiveness capable of operating over a wider range of thermal limits, which is relatively low in cost and which provides a high degree of reliability.

US. Patent 2,690,060 is an example of a prior art heat exchanger over which the heat exchanger of the present invention constitutes a substantial improvement.

According to a preferred embodiment of the invention, a heat exchanger is provided comprising an outer casing, a plurality of spaced substantially parallel tubes disposed substantially parallel to the axis of the casing and defining a first fluid path, a core member positioned in said casing and spaced from the inner wall thereof, disposed axially within said casing, said tubes being spaced from said core member, a spiral sheet disposed within said casing in the annular space between the inner wall of said casing and said core member, said spiral sheet extending axially within said casing, said tubes passing through said spiral sheet,

ice

the annular space between the inner wall of said outer casing and the outer wall of said core member, and between adjacent spirals of said spiral sheet, defining a second fluid path intersecting each of said tubes and in indirect heat exchange relation with said first fluid path.

Preferably, the adjacent spirals of the spiral sheet are disposed at an angle approaching with respect to the axis of said tubes, whereby said second fluid path noted above is disposed at an angle approaching 90 with respect to said first fluid path.

Also, in preferred practice the above noted axially disposed tubes are internally finned to provide additional heat exchange surface.

A feature of the present invention is the utilization of the combination of a spiral sheet in the annular space between the inner wall of the casing and the axially disposed core member, which defines one of the fluid flow paths, in combination with the tubes positioned in an axial direction in the casing and passing through the spiral sheet and providing the other fluid flow path, such combination permitting a wide variation of surface area between the two fluid flow paths.

Since the respective spirals of the spiral sheet can be disposed at an angle approaching 90 to the tubes passing through the spiral sheet, another feature of this invention is the essentially cross-flow heat transfer characteristics and other advantages provided by the spiral path of fluid flow for one of the fluids, e.g. the low pressure fluid, which approaches perpendicularly the fluid flow through the tubes, e.g. the high pressure fluid flow.

The invention will be more clearly understood by the description below of a preferred embodiment taken in connection with the accompanying drawing wherein:

FIG. 1 is a longitudinal cross-sectional view of the counter-flow heat exchanger according to the invention, shown partially broken away for greater clarity;

FIG. 2 is an enlarged cross-sectional view of a typical internally finned tube forming one of the two fluid flow paths within the heat exchanger, taken on line 2-2 of FIG. 1; and

FIG. 3 is a reduced perspective view of the spiral sheet in the heat exchanger of FIG. 1, with the circular apertures therein for receiving the internally finned tubes of FIG. 2, and partially defining the second or low pressure fluid flow path. 7

Referring to the drawing, particularly FIG. 1, there is shown a counter-flow heat exchanger 1, having an outer casing 2 joined by end pieces 8 to form the outer peripheral envelope of the heat exchanger. Within casing 2, there are provided tube sheets 9 and 9 positioned transversely of the casing at opposite ends thereof. Such tube sheets are suitably connected as by fusion bonding to the inner wall of casing 2 to contain within the boundaries defined by such tube sheets, one of the fluid flow paths 3, which in the present application is the low pressure flow path. The spaces 21 and 21 between the respective tube sheets 9 and 9 and end pieces 8 at opposite ends of the heat exchanger, constitute headers or plenum chambers for receiving and discharging the other fluid, in this particular application the high pressure fluid, as will be described more fully hereinafter.

A tube or core 5 passes through the heat exchanger axially thereof, for introducing and discharging one of the heat exchange fluids, that is, the low pressure fluid in the present illustrative system. Such tube 5 passes through aperture 7 in the respective end pieces 8, and is also received in apertures 10 of the respective tube sheets 9. In tube 5 there is provided a plate 6 disposed across the tube a short distance within one of the tube sheets 9, such plate serving as a blocking plate for the low pressure fluid entering through tube 5. Also provided in tube 5 are a series of peripheral apertures 19, disposed between the blocking plate 6 and the adjacent tube sheet 9 for introduction of the low pressure fluid from tube into the interior of casing 2 and between the tube sheets 9. At the opposite or discharge end of the heat exchanger there are also provided a series of peripheral apertures 19 which are located just Within the opposite tube sheet 9 for receipt of fluid from within the casing 2 for discharge through the opposite end of tube 5.

Positioned in the annular space 5 between the inner surface of the casing and the outer surface of the tube or core 5, and between the tube sheets 9 and 9 is positioned a spiral sheet 13, forming a continuous spiral passage 14 between the adjacent individual spirals 13 of the spiral sheet 13. In the embodiment illustrated in FIG. 1, it will be noted that the individual spirals 13 of the spiral sheet 13, are relatively closely positioned, forming a relatively long spiral path for the fluid passing through the spiral passage 14 from one end of casing 2 to the opposite end thereof. Containment of the fluid in the spiral passage 14 is achieved by closely fitting or sealing the outer diameter of spiral sheet 13 to the inner diameter of casing 2, and the inner diameter of spiral 13 to the outer diameter of core or tube 5. The choice of materials employed in the construction of and the sealing of the respective components of the heat exchanger are chosen to accommodate difierential thermal expansion at all temperature ranges anticipated to be encountered in the operation of the heat exchanger.

A plurality of spaced substantially parallel tubes 4 are disposed longitudinally within the casing 2. Tubes 4 have their opposite ends mounted in the tube sheets 9 and 9 and are disposed in the annular space 5 between the inner casing wall 2 and the tube 5. Tube 4 passes through apertures 14 in the respective spirals 13 of the spiral sheet 13, each of such spirals in the illustrative embodiment shown in FIG. 1 containing four of such apertures 14 for receiving four of the tubes 4 which are thus positioned around spiral sheet 13. The opposite ends of tubes 4 communicate with the headers or plenum chambers 21 and 21 at opposite ends of the heat exchanger. It will be seen that the tubes 4 have a length at least equal to the length of the spiral sheet 13 in the annular space 5 In the embodiment illustrated in FIG. 1, it will be noted that the adjacent spirals 13 of the spiral sheet 13 are disposed at an angle approaching 90 with respect to the axis of the tubes 4, so that the passages 14 defining the fluid path 3 of the low pressure fluid in annular space 5 is disposed at an angle approaching 90 with respect to the fluid, that is the high pressure fluid, passing through the tubes 4. The tubes 4 may be internally finned, as indicated at 18 in FIG. 2, to provide additional heat exchange surface.

There is also provided a fluid inlet 15 communicating with the adjacent header or plenum chamber 21 for introduction of high pressure fluid into the tubes 4, and a fluid outlet 15 at the opposite end of the heat exchanger communicating with the adjacent header or plenum cham ber 21 for discharge of high pressure fluid from the heat exchanger.

In operation, for example, high pressure fluid enters through the tubular inlet 15, which passes through apertures 16 in the respective end pieces 8 and into the plenum chamber 21 surrounding the discharge end of the tube 5. The high pressure fluid then is directed from plenum chamber 21 into the internally finned high pressure tubes 4, and during passage through the high pressure tubes 4, heat exchange occurs by passage of cold low pressure fluid through the spiral passage 14 e.g., to remove heat and lower the temperature of the high pressure fluid passing through the tubes 4, the resulting high pressure fluid of reduced temperature now being introduced into plenum 21 and discharged from plenum 21 through the high pressure fluid outlet 15 FIG. 1, passes through the apertures 19 into the annular space 5 within the casing 2 formed between the casing wall and the tube 5.'The low pressure fluid then progresses spirally through the spiral passage 14 of the spiral sheet 13, along the length of the heat exchanger, and during such flow intercepts the internally finned high pressure tubes 4 essentially perpendicularly thereof, and exiting through apertures 19 at the opposite end of the heat exchanger and being discharged through the opposite or right end of tube 5. Thus, the normally colder low pressure fluid flow circulating through passage 14 and around the outside surfaces of the internally finned tubes 4, indirectly encounters the high pressure, e.g. warmer fluid flow at such surfaces, and the resulting heat transfer occurs throughout the length of the heat exchanger. The temperature of the low pressure fluid increases through passage thereof through the heat exchanger as a result of cooling the high pressure fluid passing through the tubes 4.

Heat exchanger 1 may be constructed and assembled of materials and in a manner suited to a particular application; for example, a typical combination of materials for cryogenic service could be stainless steel for the outer casing 2, end pieces 8, tubes 5, 15 and 15 plate 6 and tube sheets 9 and 19 in combination with aluminum high pressure internally finned tubes 4 and spiral sheet 13. Spiral sheet 13 can be formed from multiple stampings of sheet aluminum in the shape of centrally perforated discs having outside and inside diameter dimensions to insure a close fit upon the outside diameter of tube 5 and the inside diameter of casing 2. The centrally perforated discs are then severed radially to form two adjacent severed edges illustrated at 13 which are then displaced from each other and fusion bonded to adjacent severed edges of another like stamping. This process is repeated until a continuous spiral or helical sheet is fabricated as illustrated in FIG. 3.

The axial length of spiral sheet 13 and the resulting linear length of the spiral flow path 3 will be dependent upon the heat exchange surface required. It is apparent therefore, that spiral sheet 13 can be fabricated to include any number of spirals 13 and the axial displacement or pitch of the spiral and the outside diameter to inside diameter ratio of the spiral sheet can be varied as desired. Optimum design of the low pressure fluid flow path depends upon the given requirements of the heat exchanger size, pressure drop and amount of heat transfer surface.

Spiral sheet 13 is then extended to the appropriate length and fixed in this portion. Apertures 14 of the required diameter are then drilled in sheet 13 to fit the outer diameter of the high pressure tubes 4. The number of apertures and tubes 4 employed will be dependent upon the thermal design of the high pressure fluid flow path which dictates the number and internal fin configuration of high pressure tubes 4.

It will be seen from the illustrative embodiment described above and shown in the drawing that the invention provides a heat exchanger in which the spiral sheet 13 constitutes a heat exchange surface of large surface area which is common to the low pressure fluid flow path through the spiral passage 14 and the high pressure fluid flow path through the tubes 4. Thus, in effect, the spiral sheet 13 formed of the respective spirals 13 constitutes external fins of large surface area for any number of the tubes 4 which are positioned through the spiral.

By provision of the spiral sheet and the spiral flow The cold low pressure fluid is directed into the heat passage 14 according to the invention, there can be afforded a wide variation in flow and temperature conditions of the respective heat exchange fluids in the fluid flow paths 3 and 4, at a relatively low capital cost, thereby providing a device having high thermal efficiency.

The heat exchanger of the invention, in addition, pro vides the advantage of a substantially perpendicular cross-flow of the fluids with respect to each other, that is, the low pressure fluid passing through the spiral passage 14 with respect to the fluid flow in the tubes 4 which are intersected by the fluid flow in the passage 14 The low pressure fluid flow in spiral passage 14 also proceeds in a direction parallel to the axis of the casing irom one end of the casing to the other.

Although in the embodiment shown and described, the colder of the two heat exchange fluids passes through tube 5 and annular space 3, if desired, the colder fluid can pass through the tubes 4. Further, the two heat exchange fluids can have the same pressure, or either fluid can have a higher pressure than the other.

It will be understood that the construction of the invention heat exchanger described above and shown in the drawing can be varied. For example, as previously noted, the number of tubes 4 and the size or spacing of the spiral passage 14 can be varied by changing the pitch of the spiral sheet 13 and varying the length thereof. Also, it will be understood that the portion of tube 5 extending between the blocking plate 6 and the apertures 19 can be a solid core member, if desired, to provide the internal peripheral wall for the inner periphery of the spiral sheet 13.

In FIGS. 3 and 4 of US. Patent 2,690,060, noted above, there are provided a number of tubes each carrying a helical ribbon or strip of metal to provide an extended heat exchange surface for the individual tubes, the respective tubes and individual helical ribbons being separated. However, this construction does not provide a common heat exchange surface for a large number of tubes, as in the case of the single spiral sheet 13 of applicants device which receives, positioned through the spiral, all of the tubes 4, through which one of the heat exchange fluids passes.

Further, in the patent device the heat exchange fluid passing externally of the tubes 49 is not confined to a positive, helical path, intersecting the respective tubes 49, because as result of the spacing between the respective tubes and the individual spirals on each of the tubes in the patent device, such fluid can pass essentially axially or vertically along the device illustrated in FIG. 3 of the patent without making substantial contact with the tubes 49 themselves. It is therefore seen that the separate helical ribbons on each tube in the patent device do not form a positive spiral path for one of the heat exchange fluids as in the present invention device, and the individual spiral ribbons in the patent device do not form a common heat exchange surface for all of the fluid in the two fluid paths, as in the device of the present invention, and there is no cross-flow of one fluid with respect to the other. Hence, the device of the present invention is substantially more efficient, more versatile and of reduced capital cost, particularly in view of the employment of but a single large spiral sheet common to all of the tubes and extending to the inner wall of the heat exchanger casing, as compared to the device disclosed in the patent.

While I have described particular embodiments of my invention for the purpose of illustration, it should be understood that various modifications and adaptations thereof may be made within the spirit of the invention, as set forth in the appended claims.

What is claimed is:

1. A heat exchanger comprising an outer casing, a plurality of spaced, substantially parallel tubes disposed substantially parallel to the axis of said casing and defining a first fluid path, a core member positioned in said casing and spaced from the inner wall thereof, said tubes being spaced from said core member, a spiral sheet disposed within said casing in the annular space between the inner wall of said casing and said core member, said spiral sheet extending axially within said casing, said tubes passing through said spiral sheet, the annular space between the inner wall of said outer casing and the outer wall of said core member, and between adjacent spirals of said spiral sheet defining a second spiral fluid path intersecting each of said tubes and in indirect heat exchange relation with said first fluid path.

2. A heat exchanger as defined in claim 1, the adjacent spirals of said spiral sheet being disposed at an angle approaching with respect to the axis of said tubes, whereby said second spiral fluid path is disposed at an angle approaching 90 with respect to said first fluid path.

3. A heat exchanger as defined in claim 1, said tubes having a length at least equal to the axial length of said spiral sheet.

4. A heat exchanger as defined in claim 1, including a first fluid inlet at one end of said heat exchanger to said annular space and to said second fluid path defined by said spiral sheet, a first fluid outlet from said second fluid path at the opposite end of said heat exchanger, a second fluid inlet to one end of said tubes at one end of said heat exchanger, and a second fluid outlet from said tubes at the opposite end of said heat exchanger.

5. A heat exchanger as defined in claim 4, including headers at opposite ends of said heat exchanger, the opposite ends of said tubes communicating with said headers, said second fluid inlet communicating with one of said headers and said second fluid outlet communicating with the other of said headers, said core member being a tubular member disposed axially within said heat exchanger, said spiral sheet being positioned around said tubular member, said tubular member passing through said headers, said first fluid inlet communicating with one end of said tubular member and said first fluid outlet communicating with the opposite end of said latter member, end members enclosing the interior of said casing from said headers, apertures in said tubular member communicating with the interior of said casing at one end of said heat exchanger, and apertures in said tubular member communicating with the interior of said casing at the opposite end of said heat exchanger.

6. A heat exchanger as defined in claim 5, the adjacent spirals of said spiral sheet being disposed at an angle approaching 90 with respect to the ends of said tubes, whereby said second spiral fluid path is disposed at an angle approaching 90 with respect to said first fluid path, said tubes having a length greater than the axial length of said spiral sheet.

References Cited UNITED STATES PATENTS 2,218,097 10/1940 Rhodes -165 X 2,287,066 6/1942 Rogers 165184 X 3,228,460 1/1966 Garwin 165-179 X 2,463,997 3/1949 Rodgers 165-179 X FOREIGN PATENTS 986,902 3/ 1965 Great Britain.

LLOYD L. KING, Primary Examiner THEOPHIL W. STREULE, Assistant Examiner US. Cl. X.R. 6213 

